Process for producing laminated film and laminated sheet

Abstract: A process for producing an extrusion laminated film or sheet is disclosed, which process uses no chemical primer and comprises a plastic substrate and a resin for extrusion laminating which process uses no chemical primer and comprises: (A) surface oxidizing at least one surface of the plastic substrate: (1) when the plastic substrate is a polyester resin, Δ (O/C) ≧ 0.08; or (2) when the plastic substrate is not a polyester resin, Δ (O/C) ≧ 0.05 wherein Δ (O/C) = (O/C)* - (O/C)°, where (O/C)° represents the ratio of the number of oxygen atoms to the number of carbon atoms on the untreated surface of the plastic substrate measured by an Electron Spectroscopy for Chemical Analysis (ESCA) method, and (O/C)* represents the ratio of the number of oxygen atoms to the number of carbon atoms on the oxidized surface of the plastic substrate measured by the ESCA method; (B) melt-extruding a resin selected from polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(metha)acrylate copolymer resins into a molten web at a temperature of from 180°C to 340°C and treating at least one surface of the molten web with ozone; and (C) contacting the oxidized surface of the plastic substrate obtained in step (A) with the ozone-treated surface of the molten web obtained in step (B), and adhering the molten web onto the substrate under pressure.

Description: The present invention relates to a process for producing an extrusion laminated film and an extrusion laminated sheet. More particularly, the present invention relates to a process for producing an extrusion laminated film and an extrusion laminated sheet with at least one resin for extrusion laminating selected from polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(meth)acrylate copolymer resins, which enables production of an extrusion laminated film and an extrusion laminated sheet comprising a plastic substrate having films firmly adhered thereto without using any chemical primer agent. Production of extrusion laminated films and sheets comprising stacked different film materials such as plastic, paper, metal foils and the like having properties in addition to those possessed by a single material, for example increased strength, gas impermeability, moisture-proofing property, heat-sealing property, improved appearance, and the like has been widely conducted and the products have primarily been used in a variety of wrappings. Such laminated films and sheets have been produced by methods such as dry laminating, wet laminating, hot laminating, extrusion laminating and coextrusion laminating, selected depending upon the characteristics to be utilized. Wrapping materials comprising a substrate having a heat-seal layer have been produced by the popularly used extrusion laminating method to form the heat-seal layer on the substrate which is advantageous in cost. Materials to be generally used for the heat-seal layer include polyolefin resins such as polyethylenes, polypropylenes, and ethylene copolymers, and ionomers. However, polyolefin resins have been used in large qualities from an economic standpoint. These resins are generally melt-extruded and laminated onto the adhesive surface of a substrate which has been precoated with a chemical primer to promote the adhesion between the substrate and the resins. The chemical primers to be used include organic titanate, organic isocyanate, and polyethyleneimine type adhesives. When used, these adhesives are usually diluted with an organic solvent such as toluene, ethyl acetate, methanol or hexane. However, these methods using chemical primers have problems such as increased production costs owing to the expense of chemical primers, the need for complicated steps of applying and drying the chemical primers, the scattering of organic solvents harmful to humans into the air when the chemical primers are dried by evaporation, causing environmental hazards in and around workplaces, the occurrence of fire due to the use of inflammable organic solvents, and limited utilization of the end film or sheet products in food wrappings owing to the odours attributable to the residual organic solvents in the chemical primers on the products. To avoid the use of chemical primers, an attempt has been made to produce a laminate by melt-kneading an ethylene copolymer produced by copolymerization of (a) ethylene, (b) unsaturated polybasic acid, and (c) an unsaturated monomer selected from lower alkyl acrylate esters, lower alkyl methacrylate esters and vinyl esters, extruding said molten copolymer at a temperature of 150 °C to 330 °C into a molten web, treating the molten web with ozone and laminating the molten web onto a substrate under pressure with the ozone treated surface of the molten web being adhered onto the surface of the substrate. This is described in JP-A-4-368845. However, only biaxially stretched nylon film was employed, and no use of ethylene-vinyl alcohol copolymers as substrate was disclosed. In addition, methods using ethylene copolymers containing unsaturated polybasic acids as the comonomer component and having an adhesive function suffer from added production costs, a lower release property in the extrusion laminating process of laminates with an increase in the amount of low melting components to limit processing temperatures as well as cumbersome exchange of resins in the extruder which may be required by the methods. Alternatively, a method for producing an extrusion laminated film by treating the surfaces of an ethylene-α-olefin copolymer molten web to be adhered onto a substrate with ozone and laminating the molten web onto the substrate without applying any chemical primer to the substrate, or a method for producing an extrusion laminated film by coextruding a modified polyolefin resin grafted with unsaturated carboxylic acids having an adhesive property onto a substrate without any chemical primer through a combination with a coextruder have been known, as disclosed in CONVERTIC (8) p. 36, (1991). However, the laminates obtained by these methods have disadvantages of insufficient adhesion strength between the laminated resin layer and the substrate limiting the area where the laminates are applied. Moreover, the method using the adhesive modified polyolefin resins grafted with unsaturated carboxylic acids requires disadvantageously the use of coextruder with an increase in production cost as well as cumbersome exchange of resins in the extruder. An object of the present invention, to overcome the aforementioned problems, is to provide a process for producing an extrusion laminated film or sheet comprising a plastic substrate and a resin for extrusion laminating selected from the group consisting of polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(meth)acrylate copolymer resins, wherein the strongly adhered laminate film or sheet can be obtained without using chemical primers which may cause aforementioned many problems. Accordingly, the present invention provides a process for producing an extrusion laminated film or sheet comprising a plastic substrate and a resin for extrusion laminating, which process uses no chemical primer and comprises: (A) surface oxidizing at least one surface of the plastic substrate such that (1) when the plastic substrate is a polyester resin, Δ (O/C) ≥ 0.08; OR (2) when the plastic substrate is not a polyester resin, Δ (O/C) ≥ 0.05; wherein Δ (O/C) = (O/C)* - (O/C)° , where (O/C)° represents the ratio of the number of oxygen atoms to the number of carbon atoms on the untreated surface of the plastic substrate measured by an Electron Spectroscopy for Chemical Analysis (ESCA) method, and (O/C)* represents the ratio of the number of oxygen atom to the number of carbon atom on the oxidised surface of the plastic substrate measured by an Electron Spectroscopy for Chemical Analysis (ESCA) method, and (O/C)* represents the ratio of the number of oxygen atoms to the number of carbon atoms on the oxidised surface of the plastic subtrate measured by the ESCA method; (B) melt-extruding a resin selected from polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(meth)acrylate copolymer resin, into a molten web at a temperature of from 180°C to 340°C and treating at least one surface of the molten web with ozone; and (C) contacting the oxidized surface of the plastic substrate obtained in step (A) with the ozone-treated surface of the molten web obtained in step (B), and adhering the molten web onto the substrate under pressure. In the accompanying drawings Figure 1 is a graph showing a variation in the value of Δ (O/C) of the surface of the corona-treated biaxially stretched nylon film with time. The plastic materials to be used as the substrate of the present invention include resins such as nylon resins, polyester resins, ethylene-vinylalcohol copolymer resins, polyvinyl alcohol resins, polypropylene resins, polyethylene resins, ethylene copolymer resins, ionomer resins, cellophane, polyvinylidene chlorides, polystyrenes, polyvinyl chlorides, polycarbonates, polymethylmethacrylates, polyurethanes, fluorinated resins, polyacrylonitriles, acetyl celluloses, polybutene resins, polyimide resins, and polyacrylate resins, which may be used alone or in combination in the form of laminate films and sheets, stretched films, coatings and fabrics. The plastic substrates may be used in the form of laminates with aluminium, iron, paper and the like stacked on the substrates with the resins being disposed in the interface therebetween. If necessary, the surfaces of the plastic substrates may be pretreated by corona discharge, plasma treatment, or flame treatment, or they may be pre-printed. The thickness of the substrates is not critical so long as the substrates can be processed by extrusion laminating, and preferably should be in the range of 1 to 10,000 µm, more preferably 5 to 500 µm. The resins for extrusion laminating to be used in the present invention may be any one or a mixture of two or more selected from polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(metha)acrylate copolymer resins. If necessary, other resins may be mixed in an amount of less than 50 % by weight. The process for producing the polyethylene resins is not critical, for example, they may be produced by radical polymerization or ion polymerization. The polyethylene resins include, for example, low density polyethylenes produced by radical polymerization, high density polyethylenes produced by ion polymerization, and ethylene-α-olefin copolymers produced by copolymerization of ethylene and α-olefins. The α-olefins to be used include, for example, α-olefins having 3 to 18 carbon atoms, such as propylene, butene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1, and octadecene-1, which may be used alone or in combination of two or more. The ethylene-α-olefin copolymers should have an α-olefin content of, preferably 1 to 30 % by weight, more preferably 5 to 20 % by weight. The process for producing polypropylene resins is not critical, and for example, they may be produced by ion polymerization. The polypropylene resins include, for example, homopolymers of propylene, copolymers of propylene with ethylene, copolymers of propylene with butene-1, and copolymers of propylene with α-olefins. For the propylene copolymers, one or more α-olefins may be used. The propylene-α-olefin copolymers should have an α-olefin content of, preferably 0.1 to 40 % by weight, more preferably 1 to 30 % by weight. Ethylene-vinylester copolymer resins and ethylene-(meth)acrylate copolymer resins may be produced by radical polymerization, e.g., by copolymerization of ethylene with radically copolymerizable monomers. Vinyl esters for the ethylene-vinylester copolymers include, for example, vinyl acetate and vinyl propionate. (Meth)acrylates for the ethylene-(meth) acrylate copolymers include, for example, acrylates having 4 to 8 carbon atoms such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, and methacrylates having 4 to 8 carbon atoms such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, and isobutyl methacrylate. One or more of these comonomers may be used. Ethylene-vinylester copolymers and ethylene-(meth)acrylate copolymers should have a comonomer content of, preferably, not higher than 30 % by weight, more preferably not higher than 20 % by weight. A content of comonomer to be copolymerized with ethylene which is higher than 30 % by weight results in an unpleasant odour of the laminate films and sheets, rendering them unsuitable for food wrapping materials as well as increasing the production cost, although there is no problem in the adhesiveness to the substrate, the primary object of the present invention. Polyethylene resins, ethylene-vinylester copolymer resins, and ethylene-(meth)acrylate copolymer resins typically have a melt flow rate (MER) at 190 °C in the range of 1 to 100 g/10 min., and polypropylene resins typically have a MER at 230 °C in the range of 1 to 100 g/10 min. The surface oxidizing step (A) of the present invention comprises subjecting at least one of the surfaces of the plastic substrate to surface oxidizing treatment to generate at least a predetermined level of oxidation activated sites, thereby affording strong adhesion. The term "at least a predetermined level of oxidation activated sites" is defined by Δ (O/C) as explained below. Namely, the conditions of the treatment are expressed by the following formula: (1) When the plastic substrate is of polyester resins, Δ (O/C) ≧ 0.08 (2) When the plastic substrate is of other materials than polyester resins, Δ (O/C) ≧ 0.05 with Δ (O/C) = (O/C)* - (O/C)° , where (O/C)° represents the ratio of the number of oxygen atoms to the number of carbon atom on the untreated surface of the plastic substrate measured by an ESCA method, and (O/C)* represents the ratio of the number of oxygen atoms to the number of carbon atoms on the oxidized surface of the plastic substrate measured by the ESCA method. In a preferred process of the invention, (1) When the plastic substrate is a polyester resin, Δ (O/C) ≧ 0.10; or (2) When the plastic substrate is not a polyester resin, ▵ (O/C) ≧ 0.07 with Δ (O/C) = (O/C)* - (O/C)° , where (O/C)° and (O/C)* are as defined above. The (O/C)* is a value obtained by conducting the measurement at 30 minutes after the plastic substrate was subjected to the surface oxidizing treatment according to the present invention and a molten were made of the resins for extrusion laminating was adhered onto the substrate. Practically a plastic substrate which has been subjected to the surface oxidizing treatment, but which has no molten web adhered was additionally provided and measured. The term ESCA means Electron Spectroscopy for Chemical Analysis, and (O/C)* and (Q/C)° are determined as follows: The product of the area of the peak in strength by the relative sensitivity of the peak is determined for each of O 15 and C 15 , and the ratio of existing oxygen and carbon atoms (O/C)° is determined from both the products. Further details of the determination are given, for example, by IKADA YOSHIHITO in "Fundamental and Application of Surfaces of Polymers (I)" (KAGAKU DOJIN Publisher, 1986) Section 4. Variation of Δ (O/C) with time is explained below. Figure 1 shows the variation of Δ (O/C) with time for the case where the plastic substrate was a biaxially stretched nylon film and the surface oxidizing treatment was effected with corona discharge. As clearly seen from the Figure, the value of Δ (O/C) is rapidly reduced with time, for example,it becomes lower than 0.05 after one day at a corona density of 100 W· min./m 2 and it becomes actually lower than 0.05 at 30 W·min./m 2 when the corona discharge is performed not in-line with the ozone-treatment step and the pressured laminating step, thus causing insufficient adhesive strength to be achieved. Similarly when the substrate is of polyester resins, the value of Δ (O/C) is lower than 0.08, causing insufficient adhesive strength to be achieved. That is, when the value of Δ (O/C) is excessively small, one can not achieve sufficient adhesive strength. The polyester resins are polymer resins obtained by condensation polymerization of aromatic dicarboxylic acids such as terephthalic acid, and 2,6-naphthalene dicarboxylic acid, with aliphatic glycols such as ethylene glycol, diethylene glycol, and 1,4-cyclohexane dimethanol. Representative examples of such polymers are polyethylene terephthalate (PET), polyethylene 2,6-naphthalene dicarboxylate (PEN), and polybutylene terephthalate (PBT). The polymers may be those containing not higher than 20 mole % of the third components other than said polymers. In this case, dicarboxylic acid components to be used include, for example, isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, and p-oxybenzoic acid and the like), which may be used alone or in combination of two or more. The glycol components to be used include ethylene glycol, propylene glycol, butane diol, 1,4-cyclohexane dimethanol, and neopentyl glycol, which may he used alone or in combination of two or more. Although there are commercially available plastic substrates which have been subjected to surface oxidizing treatment such as corona discharge, for improving printability of the surfaces, such commercial products can not achieve such sufficient strong adhesion as intended by the present invention, if they were used as they are without conducting the surface oxidizing treatment of the present invention. The surface oxidizing step (A) may be performed in practice by any one of treatments with (a 1 ) corona discharge, (a 2 ) plasma, (a 3 ) flame plasma, (a 4 ) electron beam irradiation, or (a 5 ) UV irradiation, as described in detail later. The ozone-treating step (B) comprises melt-extruding a resin for extrusion laminating into a molten web at a temperature of 180 °C to 340 °C and subjecting at least one of the surfaces of the film to a treatment with ozone. The treatment with ozone may be performed by, for example, blowing a gas such as containing ozone from a nozzle or slit like blowing opening in a lower open gap disposed under a T die onto the extruded molten web. When the ozone nozzle can not be disposed under the T die, the gas may be blown onto the plastic substrate immediate before laminating under pressure. The amount of ozone to be blown should preferably be not less than 1.0 mg per square meter of the surface of the extruded molten web which is being transferred, more preferably not less than 10.0 mg/m 2 . The resins for extrusion laminating are melt-extruded into a molten web at a temperature of 180 °C to 340 °C. A temperature lower than 180 °C may result in poor stretchability of the molten webs, make it difficult to produce uniform thickness of molten web, and cause insufficient adhesive strength with the plastic substrate. On the other hand, a temperature higher than 340 °C may produce severer oxidation of the surfaces of the molten webs and worse odor of the webs. Preferred resin temperature is from 210 to 330°C. The pressurized laminating step (C) according to the present invention comprises contacting the oxidized surface of the plastic substrate obtained in the surface oxidizing step with the ozone-treated surface of the molten web obtained in the ozone-treating step, and adhering the film onto the substrate under pressure while maintaining for the oxidized surface of the plastic substrate to be adhered under pressure. For the pressurized laminating step of the present invention, one may use any known extrusion laminator. In one aspect of the present invention, steps (A) and (C) are carried out in-line such that the plastic substrate is transferred to step (C) immediately after the end of step (A). In this way a high level of adhesive strength can be development to prevent undesirable blocking of the plastic substrate. The aforementioned reference to conducting steps (A) and (C) in-line means that the extrusion laminating process is accomplished by using an apparatus where the plastic substrate is sent out to be transferred through (A) the surface oxidizing step, (C) the pressurized laminating step, and the product winding step which are sequentially disposed in the same line along the flow path of the plastic substrate and which are promptly conducted in one sequential operation. In another aspect of the present invention, the process comprises, before step (A), a preheating step (A 0 ) where the plastic substrate is heated to a temperature not lower than 40°C, but not higher than its melting point. This is in order to further improve the adhesive strength. The heating temperature should not be lower than 40°C, but not higher than the melting point of the plastic substrate, preferably not lower than 60°C to 30°C lower than the melting point of the plastic substrate. The heating temperature refers to the surface temperature of the plastic substrate which may be measured by, for example, a contact type thermometer. If the heating temperature is too low, the resulting laminate films or sheets may attain insufficient improvement in adhesive strength between the plastic substrate and the extrusion laminated layer, while the heating temperature is too high, there may be produced problems of shrinking or curling of the laminated film. Most suitable heating of the plastic substrate may be achieved by using far infrared ray heaters or heating rollers. For example, the plastic substrate may be passed under a far infrared ray heater in the course of transferring the plastic substrate to the surface oxidizing treatment step. For example, a plastic substrate having a width of 500 mm may be heated for 0.05 to 5 seconds at a distance between the surface of the plastic substrate and the heater of about 1 to 30 cm using a far infrared ray heater having an output of about 1 to 30 KW (when a plurality of heaters are used, the total output thereof). The process of the present invention may further comprise, after step (C), an aging step (D) wherein the extrusion laminated film or sheet is aged in a warm atmosphere. This further improves the adhesive strength. The aging temperature should not be lower than 30 °C, but less that 50°C, preferably 40 to 45°C. Too low an again temperature may attain insufficient improvement in adhesive strength, while too high an aging temperature may result in reduced heat-seal performance and reduced hot-tack performance, and moreover, may produce curling of laminate film and inconveniences in a slitting step and a content filling step, denaturation of the laminated films, and odour problems. The aging time should usually be 1 to 120 hours, preferably 10 to 120 hours. Too short an aging time may attain insufficient improvement in adhesive strength, while too long an aging time may result in denaturation of the laminated films and disadvantageous productivity. The aging step (D) may be accomplished by using an ordinary oven or a temperature-controllable chamber. The process of the present invention can comprise a combination of the preheating step (A ° ), the surface oxidizing step (A), the ozone-treating step (B), the pressurized laminating step (C) and the aging step (D) to achieve stronger adhesive strength. Next, embodiments of (A) the surface oxidizing step are described under. The surface oxidizing step is conducted in practice by treatments using any one of (a 1 ) corona, (a 2 ) plasma, (a 3 ) flame plasma, (a 4 ) electron beam irradiation, or (a 5 )UV irradiation. Preferably the step (A) is effected by (a 1 ) treating at least one surface of the plastic substrate with a corona discharge. The corona discharge treatment may be conducted by passing the plastic substrate through a corona atmosphere generated with known corona discharging apparatus. In order to achieve a high level of adhesive strength, preferably the corona discharge density should not be less than 40 (W.min./m 2 ), more preferably not less than 50 (W.min./m 2 ). When the surface oxidatively preheating step and/or the aging step are used, the preferred corona discharge density is 10 (W.min./m 2 ) or more. In one preferred aspect, the process of the invention comprises a preheating step (A 0 ) as defined above before the surface oxidising step (A), and which further comprises effecting the step (A) by the corona discharge step (a,) defined above, wherein the corona discharge density is not less than 10W.min/m 2 . In another preferred aspect, the process of the invention comprises an aging step (D) as defined above after the pressurized laminating step (C), and which further comprises effecting the surface oxidizing step (A) by the corona discharge treatment step (a 1 ) as defined above wherein the corona discharge density is not less than 10 W.min./m 2 . In a further preferred aspect, the process of the invention comprises a preheating step (A 0 ) as defined above before the surface oxidixing step (A), and an aging step (D) as defined above after the pressurised laminating step (C); and which further comprises effecting the surface oxidising step (A) by the corona discharge treatment step (a 1 ) as defined above, wherein the corona discharge density is not less than 10W.min./m 2 . The plasma-treating step (a 2 ) may be performed by exciting electronically a single gas such as argon, helium, krypton, xenon, hydrogen, nitrogen and air, or a mixture of gases with plasma jet, then removing charged particles, and blowing the produced electrically neutral excited inert gases onto the surface of the plastic substrate. The flame plasma-treating step (a 3 ) may be performed by blowing the plasma generated by ionization of the flame from combustion of naturally occurring gases or propane. The electron beam irradiation step (a 4 ) may be carried out by irradiating the surface of the plastic substrate with an electron beam generated with an electron accelerator. As the electron beam irradiation apparatus, one may employ, for example, an apparatus under the tradename "ELECTROCURTAIN" which is capable of irradiating curtain-like uniform electron beams from a linear filament. The UV irradiating treatment step (a 5 ) may be conducted by, for example, irradiating the surface of the plastic substrate with ultraviolet radiation having a wavelength of 200 to 400 µm. In the present invention, the resin extrusion laminated onto the plastic substrate may be applied to the heat-seal layer of the laminate films or sheets or to the intermediate layer of the laminate films or sheets depending upon the resin's functions such as easily heat-sealable property and moisture proofing property. Moreover, the present invention can apply to a sandwich type extrusion laminating method to form a laminate. To the resins for extrusion laminating used in the present invention, there may be added known additives such as anti-oxidant agents, anti-blocking agents, weather-resisting agents, neutralizing agents, flame retarding agents, antistatic agents, anti-fogging agents, sliding agents, dispersants, pigments, organic or inorganic fillers. The extrusion laminated films and sheets of the present invention have utility in wrapping materials such as food wrapping materials and medicine packaging materials as well as industrial materials. The present invention is further illustrated with reference to the following examples. Example 1 A low density polyethylene (LDPE, available from Sumitomo Chemical Industry Co. Ltd., under tradename "SUMIKATHENE", L716-H MFR 7 g/10 min., Density: 0.919 g/cm 3 ) was melt-kneaded with an extruder having an aperture diameter of 65 mm and extruded through a T die at a resin temperature of 315 °C into a molten web having a width of 450 mm a thickness of 50 µ at an extrusion laminating speed of 80 m/min., and an ozone-containing air was blown to the surface of the molten web to be adhered onto the substrate through a nozzle disposed at a distance of 30 mm from the bottom of the die to achieve treatment of the contact surface of the molten web with ozone. The amount of ozone used for the treatment was 37 mg/m 2 . Then the molten web was laminated onto a 15 µ biaxially stretched EVOH (ethylene-vinylalcohol copolymer) film which had been modified by treating the surface thereof with corona discharge at a treatment density of 103 W·min./m 2 with a corona discharge apparatus provided in-line with the extrusion laminater to produce a laminate film. The produced laminate film was evaluated for various properties as follows. The results of the evaluation and the processing conditions are summarized in Table 1. (1) Determination of (O/C)* and (O/C)° By using ESCALABMK-II available from FI Surface Science System Co., the ratio of existing oxygen and carbon atoms (O/C) is determined from the product of the area of the peak in strength by the relative sensitivity for O 15 and that for C 15 . The (O/C)* was the value of measurement at 30 minutes after the substrate was subjected to the surface oxidizing treatment (corona discharge treatment) and the resin for extrusion laminating was adhered onto the substrate. Practically a plastic substrate which has been subjected to the surface oxidizing treatment at the same time with the laminated products, but which has no molten web laminated was additionally provided and measured for the surface thereof. (2) Determination of film adhesion strength The film adhesiveness was evaluated from the peeling strength when a laminate film of 15 mm in width was peeled at 180° at a pulling speed of 200 mm/min. with an autostrain type tensile tester available from Toyo Seiki Co. Ltd. Examples 2 to 14 and Comparative Examples 1 to 24 Example 1 was repeated, except that the conditions as shown in Tables 1 to 3 and Tables 7 to 11 were used. In Examples 5, 6, 10, and Comparative Examples 4, 5, 12, 13 and 14, the melt-kneading was effected with two extruders having an aperture diameter of 65 mm to extrude the same LDPE through a multi-slot T die into a molten web having a total thickness of 60 µ (30 µ each). In Examples 7, 13, and Comparative Examples 9, 10, 22, 23 and 24, the same procedure as above was employed to provide LDPE or EMMA for a layer contacting with the plastic substrate and LLDPE for a sealant layer which were coextruded to form a laminate. The results of the evaluation and the processing conditions are summarized in Tables 1 to 3 and Tables 7 to 11, in which the column heading "-" represents no treatment effected. Examples 15 to 17 In Example 15, a linear low density polyethylene (LLDPE, available from Sumitomo Chemical Industry Co. Ltd., under tradename "SUMIKATHENE α " CS8026 MFR 10 g/10 min., Density: 0.914 g/cm 3 ) was melt-kneaded with two extruders having an aperture diameter of 65 mm and extruded through a multi-slot T die at a resin temperature of 290 °C into a molten web having a width of 450 mm and a total thickness of 60 µ (30 µ each) at an extrusion laminating speed of 140 m/min., and an ozone-containing air was blown to the surface of the molten web to be adhered onto the substrate through a nozzle disposed at a distance of 30 mm from the bottom of the die to achieve treatment of the contact surface of the molten web with ozone. The amount of ozone used for the treatment was 21 mg/m 2 . Then using a corona preheating apparatus and a corona discharge apparatus which were provided in-line with the extrusion laminater, the treatments were performed as follows: A substrate was heated with far infrared ray heater (9.6 KW output) keeping the distance between the substrate and the heater of 10 cm. At this time, the temperature of the surface of the substrate was 90 °C as measured by a surface contact type thermometer. Then there was produced as a substrate a biaxially stretched nylon film having a thickness of 15 µm and a width of 500 mm which had been modified by treating the surface thereof with corona discharge at a treatment density of 59 W·min./m 2 in an atmosphere of air with a corona discharge apparatus. Then the molten web after the treatment with ozone was laminated onto said substrate treated with corona discharge. In Example 16, there were provided EMMA for an adhesive layer with the plastic substrate and LLDPE for a sealant layer to produce laminate films having a total thickness of 60 (30 µ each). The produced laminate films were evaluated for various properties. The results of the evaluation and the processing conditions are summarized in Table 4. Examples 18 to 26 (Examples where an aging step was practiced) In Example 18, a linear low density polyethylene (LLDPE, available from Sumitomo Chemical Industry Co. Ltd., under tradename "SUMIKATHENE α " CS8026 MFR 10 g/10 min., Density: 0.914 g/cm 3 ) was melt-kneaded with two extruders having an aperture diameter of 65 mm and extruded through a multi-slot T die at a resin temperature of 290 °C into a molten web having a width of 450 mm and a total thickness of 60 µ (30 µ each) at an extrusion laminating speed of 140 m/min., and an ozone-containing air was blown to the surface of the molten web to be adhered onto the substrate through a nozzle disposed at a distance of 30 mm from the bottom of the die to achieve treatment of the contact surface of the molten web with ozone. The amount of ozone used for the treatment was 21 mg/m 2 . Then the molten web was laminated onto a 15 µ biaxially stretched nylon substrate which had been modified by treating the surface thereof with corona discharge at a treatment density of 25 W·min./m 2 with a corona discharge apparatus provided in-line with the extrusion laminater. The produced laminate film was aged at 45 °C for 120 hours in an atmosphere of air to improve adhesive strength of the laminated film. In Examples 20, 21 and 26, there were provided LDPE or EMMA for an adhesive layer with the plastic substrate and LLDPE for a sealant layer to produce laminate films having a total thickness of 60 (20/40 µ, or 30/30 µ). In Examples 23, 24 and 25, using the similar procedure, there were produced LDPE single layer laminates. The produced laminate films were evaluated for various properties. The results of the evaluation and the processing conditions are shown in Tables 5 to 6. Example 1 2 3 4 5 Plastic substrate*1 EVOH EVOH CEVOH CEVOH ONy Resin for extrusion laminating*2 LD LL LL LL LL Process conditions Melt-extrusion temperature (°C) 315 295 295 260 290 Speed (m/min.) 80 120 120 80 80 Thickness (µ) 50 40 40 50 60 Corona discharge treatment Treatment density (W·min/m 2 ) 103 69 69 103 15 (O/C)* 0.413 0.410 0.332 0.339 0.230 (O/C)° 0.314 0.314 0.238 0.238 0.153 Δ (O/C) 0.099 0.096 0.094 0.101 0.077 Ozone treatment Treatment amount (mg/m 2 ) 37 25 25 37 37 Evaluation Peel adhesion strength (g/15mm) Could not be separated 340 Example 6 7 8 9 10 Plastic substrate*1 ONy ONy ONy ONy PET Resin for extrusion laminating*2 LL LD LD EMMA LL LL Process conditions Melt-extrusion temperature (°C) 290 315 315 300 290 290 Speed (m/min.) 140 80 80 80 80 Thickness (µ) 60 20 40 40 60 40 Corona discharge treatment Treatment density (W·min/m 2 ) 59 103 103 103 103 (O/C)* 0.242 0.245 0.245 0.245 0.570 (O/C)° 0.153 0.153 0.153 0.153 0.402 Δ (O/C) 0.089 0.092 0.092 0.092 0.168 Ozone treatment Treatment amount (mg/m 2 ) 21 37 37 37 37 Evaluation Peel adhesion strength (g/15mm) 600 610 520 Resin break 450 Example 11 12 13 14 Plastic substrate*1 PET PET CNy CNy Resin for extrusion laminating*2 LD EMMA LD LD LL Process conditions Melt-extrusion temperature (°C) 315 300 315 315 290 Speed (m/min.) 80 80 80 80 Thickness (µ) 40 40 20 40 30 Corona discharge treatment Treatment density (W·min/m 2 ) 15 103 103 103 (O/C)* 0.503 0.570 0.220 0.220 (O/C)° 0.402 0.402 0.158 0.158 Δ (O/C) 0.101 0.168 0.062 0.062 Ozone treatment Treatment amount (mg/m 2 ) 37 37 37 37 Evaluation Peel adhesion strength (g/15mm) 320 350 360 390 Example 15 16 17 Plastic substrate*1 ONy ONy PET Resin for extrusion laminating*2 LL EMMA LL LL Process conditions Melt-extrusion temperature (°C) 290 290 290 290 Speed (m/min.) 140 140 140 Thickness (µ) 60 30 60 30 Corona discharge treatment Treatment density (W·min/m 2 ) 59 59 59 (O/C)* 0.242 0.242 0.535 (O/C)° 0.153 0.153 0.402 Δ (O/C) 0.089 0.089 0.133 Ozone treatment Treatment amount (mg/m 2 ) 21 21 21 Corona preheating temperature (°C) 90 80 90 Evaluation Peel adhesion strength (g/15mm) 670 990 480 Example 18 19 20 21 22 Plastic substrate*1 ONy ONy ONy ONy PET Resin for extrusion laminating*2 LL LL LD EMMA LL LL LL Process conditions Melt-extrusion temperature (°C) 290 290 315 290 290 290 290 Speed (m/min.) 140 140 140 140 80 Thickness (µ) 60 60 20 30 60 40 30 Corona discharge treatment Treatment density (W·min/m 2 ) 25 59 59 25 15 (O/C)* 0.238 0.242 0.242 0.218 0.503 (O/C)° 0.153 0.153 0.153 0.153 0.402 Δ (O/C) 0.085 0.089 0.089 0.065 0.101 Ozone treatment Treatment amount (mg/m 2 ) 21 21 21 21 37 Aging treatment Temperature (°C) 45 45 40 45 45 Time (hr.) 120 48 12 120 120 Evaluation Peel adhesion strength (g/15mm) 550 730 640 1010 630 Example 23 24 25 26 Plastic substrate*1 PET PVA PVA CNy Resin for extrusion laminating*2 LD LD LD LD LL Process conditions Melt-extrusion temperature (°C) 315 315 315 315 290 Speed (m/min.) 80 80 80 80 Thickness (µ) 40 40 40 20 40 Corona discharge treatment Treatment density (W·min/m 2 ) 15 29 103 103 (O/C)* 0.503 0.512 0.524 0.220 (O/C)° 0.402 0.447 0.447 0.158 Δ (O/C) 0.101 0.065 0.077 0.062 Ozone treatment Treatment amount (mg/m 2 ) 37 37 37 21 Aging treatment Temperature 45 45 45 40 Time (hr.) 120 120 120 72 Evaluation Peel adhesion strength (g/15mm) 470 360 400 640 Comparative Example 1 2 3 4 5 Plastic substrate*1 EVOH EVOH CEVOH ONy ONy Resin for extrusion laminating*2 LD LL LL LL LL Process conditions Melt-extrusion temperature (°C) 315 295 295 290 290 Speed (m/min.) 80 80 80 140 140 Thickness (µ) 50 40 40 60 60 Corona discharge treatment Treatment density (W·min/m 2 ) - 103 103 - 59 (O/C)* 0.329 0.413 0.339 0.191 0.242 (O/C)° 0.314 0.314 0.238 0.153 0.153 Δ (O/C) 0.015 0.099 0.101 0.038 0.089 Ozone treatment Treatment amount (mg/m 2 ) - - - 21 - Corona preheating Temperature (°C) - - - - 90 Evaluation Peel adhesion strength (g/15mm) 30 40 40 210 < 5 Comparative Example 6 7 8 9 10 Plastic substrate*1 ONy ONy ONy ONy ONy Resin for extrusion laminating*2 LD LD LD EMMA EMMA LL LL Process conditions Melt-extrusion temperature (°C) 315 315 315 290 290 Speed (m/min.) 120 120 120 140 140 Thickness (µ) 40 40 40 30 30 30 30 Corona discharge treatment Treatment density (W·min/m 2 ) - - 69 - 59 (O/C)* 0.191 0.191 0.243 0.191 0.242 (O/C)° 0.153 0.153 0.153 0.153 0.153 Δ (O/C) 0.038 0.038 0.090 0.038 0.089 Ozone treatment Treatment amount (mg/m 2 ) - 25 - - - Corona preheating Temperature (°C) - - - - 80 Evaluation Peel adhesion strength (g/15mm) 100 260 260 40 60 Comparative Example 11 12 13 14 15 Plastic substrate*1 ONy PET PET PET PET Resin for extrusion laminating*2 EMMA LL LL LL LD Process conditions Melt-extrusion temperature (°C) 300 290 290 290 315 Speed (m/min.) 80 80 80 80 80 Thickness (µ) 40 60 60 60 40 Corona discharge treatment Treatment density (W·min/m 2 ) - - - 103 - (O/C)* 0.191 0.469 0.469 0.570 0.469 (O/C)° 0.153 0.402 0.402 0.402 0.402 Δ (O/C) 0.038 0.067 0.067 0.168 0.067 Ozone treatment Treatment amount (mg/m 2 ) - - 37 - - Evaluation Peel adhesion strength (g/15mm) 260 < 5 210 < 5 90 Comparative Example 16 17 18 19 20 Plastic substrate*1 PET PET PET PVA PVA Resin for extrusion laminating*2 LD LD EMMA LD LD Process conditions Melt-extrusion temperature (°C) 315 315 300 315 315 Speed (m/min.) 80 80 80 80 80 Thickness (µ) 40 40 40 40 40 Corona discharge treatment Treatment density (W·min/m 2 ) - 103 - - - (O/C)* 0.469 0.570 0.469 0.460 0.460 (O/C)° 0.402 0.402 0.402 0.447 0.447 Δ (O/C) 0.067 0.168 0.067 0.013 0.013 Ozone treatment Treatment amount (mg/m 2 ) 37 - - - 37 Evaluation Peel adhesion strength (g/15mm) 240 280 270 30 60 Comparative Example 21 22 23 24 Plastic substrate*1 PVA CNy CNy CNy Resin for extrusion laminating*2 LD LD LD LD LL LL LL Process conditions Melt-extrusion temperature (°C) 315 315 315 315 290 290 290 Speed (m/min.) 80 80 80 80 Thickness (µ) 40 20 20 20 30 30 30 Corona discharge treatment Treatment density (W·min/m 2 ) 103 - - 103 (O/C)* 0.524 0.185 0.185 0.220 (O/C)° 0.447 0.158 0.158 0.158 Δ (O/C) 0.077 0.027 0.027 0.062 Ozone treatment Treatment amount (mg/m 2 ) - - 37 - Evaluation Peel adhesion strength (g/15mm) 190 140 180 270 *1 Plastic substrate EVOH: Biaxially stretched EVOH (ethylene-vinylalcohol copolymer), EF-XL type 15 µ, available from Kuraray Co.Ltd. CEVOH: Unstretched EVOH, EF-E type 20 µ, available from Kuraray Co. Ltd. ONy: Biaxially stretched nylon, ON type 15 µ, available from Unichika Co. Ltd. CNy: Unstretched nylon, General type 25 µ, available from Toray Co. Ltd. PET: Biaxially stretched polyester, E5100 type 25 µ, available from Toyoboseki Co. Ltd. PVA: Biaxially stretched polyvinylalcohol, BOBRON 25 µ, available from Nichigo Film Co. Ltd. The data in the item "Corona discharge treatment" represent the corona treatments performed according to the present invention independently of corona treatments which might be effected to commercially available films before purchased. *2 Resins for extrusion laminating LL: LLDPE linear low density polyethylene, available from Sumitomo Chemical Industry Co. Ltd., under tradename "SUMIKASEN", α CS8026, MFR 10 g/10 min., Density: 0.914 g/cm 3 . LD: LDPE low density polyethylene, available from Sumitomo Chemical Industry Co. Ltd., under tradename "SUMIKASEN", L716-H MFR 7 g/10 min., Density: 0.919 g/cm 3 . EMMA: ethylene-methylmethacrylate copolymer, available from Sumitomo Chemical Industry Co. Ltd., under tradename "AKURIFT", WH302 MFR 7 g/10 min., Density: 0.930 g/cm 3 ; Content of methylmethacrylate: 15 wt.%. The mark "-" represents that the treatment was not conducted.

Claims: A process for producing an extrusion laminated film or sheet comprising a plastic substrate and a resin for extrusion laminating, which process uses no chemical primer and comprises: (A) surface oxidizing at least one surface of the plastic substrate such that: (1) when the plastic substrate is a polyester resin, Δ (O/C) ≥ 0.08; or (2) when the plastic substrate is not a polyester resin, Δ (O/C) ≥ 0.05; wherein Δ (O/C) = (O/C)* - (O/C)° , where (O/C)° represents the ratio of the number of oxygen atoms to the number of carbon atoms on the untreated surface of the plastic substrate measured by an Electron Spectroscope for Chemical Analysis (ESCA) method, and (O/C)* represents the ratio of the number of oxygen atoms to the number of carbon atoms on the oxidized surface of the plastic substrate measured by the ESCA method; (B) melt-extruding a resin selected from polyethylene resins, polypropylene resins, ethylene-vinylester copolymer resins and ethylene-(meth)acrylate copolymer resins into a molten web at a temperature of from 180° to 340°C and treating at least one surface of the molten web with ozone; and (C) contacting the oxidized surface of the plastic substrate obtained in step (A) with the ozone-treated surface of the molten web obtained in step (B), and adhering the molten web onto the substrate under pressure, wherein step (C) is conducted whilst maintaining the values of Δ (O/C) such that Δ (O/C) is ≥ 0.08 when the plastic substrate is polyester resin and Δ (O/C) ≥ 0.05 when the plastic substrate is not a polyester resin. A process according to claim 1, wherein: (1) when the plastic substrate is a polyester resin, Δ (O/C)≥ 0.10; or (2) when the plastic substrate is not a polyester resin, Δ (O/C) ≥ 0.07 A process according to claim 1 or 2, wherein steps (A) and (C) are carried out in-line such that the plastic substrate is transferred to step (C) immediately after the end of step (A). A process according to claim 1, 2 or 3, comprising, before step (A), a preheating step (A 0 ), wherein the plastic substrate is heated to a temperature not lower than 40°C, but not higher than its melting point. A process according to any one of the preceding claims comprising, after step (C), an aging step (D) wherein the extrusion laminated film or sheet is aged in a warmed atmosphere. A process according to claim 5, wherein the aging step (D) is carried out at a temperature not lower than 30°C, but less than 50°C. A process according to any one of the preceding claims, wherein step (A) is effected by: (a 1 ) treating at least one surface of the plastic substrate with a corona discharge. A process according to claim 1, wherein the corona discharge density in step (a 1 ) is not less than 10 W·min./m 2 . A process according to claim 1, which comprises a preheating step (A 0 ) as defined in claim 4 before the surface oxidizing step (A), and which further comprises effecting the surface oxidizing step (A) by the corona discharge treatment step (a 1 ) defined in claim 8, wherein the corona discharge density is not less than 10 W·min./m 2 . A process according to claim 1, which comprises an aging step (D) as defined in claim 5 after the pressurized laminating step (C), and which further comprises effecting the surface oxidizing step (A) by the corona discharge treatment step (a 1 ) as defined in claim 8, wherein the corona discharge density is not less than 10 W·min./m 2 . A process according to claim 1, which comprises a preheating step (A 0 ) as defined in claim 4 before the surface oxidizing step (A), and an aging step (D) as defined in claim 5 after the pressurized laminating step (C); and which further comprises effecting the surface oxidizing step (A) by the corona discharge treatment step (a 1 ) as defined in claim 8, wherein the corona discharge density is not less than 10 W·min./m 2 . A process according to claim 1, wherein the surface oxidizing step (A) is effected by: (a 2 ) subjecting at least one surface of the plastic substrate to treatment with plasma. A process according to claim 1, wherein the surface oxidizing step (A) is effected by: (a 3 ) subjecting at least one surface of the plastic substrate to treatment with flame plasma. A process according to claim 1, wherein the surface oxidizing step (A) is effected by: (a 4 ) irradiating at least one surface of the plastic substrate with an electron beam. A process according to claim 1, wherein the surface oxidizing step (A) is effected by: (a 5 ) irradiating at least one of the surfaces of the plastic substrate with ultraviolet radiation. A process according to any one of the preceding claims wherein the plastic substrate is a nylon resin or an ethylene-vinyl alcohol copolymer resin.

Inventors: GOTOH YUJI, HAYASHIDA HARUO, ISHIBASHI FUMIO, KUBO KOHJI, TAKAHATA HIROAKI, GOTOH, YUJI, HAYASHIDA, HARUO, ISHIBASHI, FUMIO, KUBO, KOHJI., TAKAHATA, HIROAKI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1994
Main classification: B29C47
IPC codes: C08J7, B29C47, B29C35, B29C59, B29C43, B32B37, C08J5